CHD (compressed hunks of data) They represent a CD DVD or hard drive. Now for most items in MAME you will need both some ROMs and CHDs. The ROMs usually in th

CHD (compressed hunks of data) They represent a CD DVD or hard drive. Now for most items in MAME you will need both some ROMs and CHDs. The ROMs usually in that case are the firmware of the device that loads up the CHD. The arcade platforms basically ended up being fairly beefy PCs or in some cases retooled game consoles. At one point the ROMs for those devices were split out into their own torrent. They usually represent something like an playstation. With the CHDs being the CDs. It is also used in places like the Atari platform that runs some of its hardware that has basically different hard drives and some roms to switch out the board being the same between all the arcade games. It is also used for laserdisc games but those probably will change in the next few years as the doomsday project gets its preservation setup the way they want it. In the laserdisc game it would represent the console the arcade game used to load up the disc. Many of the emus out there are adopting the CHD format for CD/DVD support.